3D printing brush is inverted

[appsforartists]

If you enable experimental brushes in the APK and try the 3D printing brush on the last page, the environment inverts (with the sky turning bright grey instead of dark). The occlusion inverts too, with the mountains being composited in front of the model, so you can only see things painted in the sky.

[andybak]

Yep. I've been meaning to look at this for a while now but other things have taken priority. Thanks for reporting it. Maybe someone else will take a look before I manage to get around to it.